Nitrogen Dynamics in Soi‐Plant Systems

Nitrogen plays a key role in plant nutrition. Nitrogen is currently the most widely used fertilizer nutrient and the demand for it is likely to grow in the foreseeable future. Nitrogen mineralized from the soil organic pool often constitutes a large part of the N available to the crop. The N model comprises four subroutines describing N movement, soil N transformations, N uptake, and plant N stress factors. Fertilizer N is partitioned in the model between nitrate, ammonium, and urea pools according to the nature of the fertilizer used. The approach used in the CERES models calculates the components of crop demand for N and the soil supply of N separately, and then uses the lesser of these two to determine the actual rate of uptake. In subroutine NTRANS, the CERES model simulates the decay of organic matter and the subsequent mineralization and/or immobilization of N, the nitrification of ammonium, and denitrification.